The present invention relates to a system and a method for starting a pump, and in particular to a starting in an environment of a low temperature.
Japanese Unexamined Patent Publication No. 2003-178782 discloses a fuel cell system which generates electricity through reaction of hydrogen gas and air. A part of the hydrogen gas which is supplied to a hydrogen electrode of a fuel cell stack is often contained in hydrogen off-gas without being reacted and is exhausted from the fuel cell stack. To effectively utilize the unreacted hydrogen gas, such a system is proposed that a hydrogen pump circulates the hydrogen off-gas to the hydrogen electrode of the fuel cell stack.
However, since water is produced with generation of electricity in the fuel cell system and this water is exhausted from the fuel cell stack with the hydrogen off-gas, moisture is introduced into the hydrogen pump with the hydrogen off-gas. Therefore, if the operation of the fuel cell system is stopped in an environment of a low temperature, there is fear that the moisture in the hydrogen pump condenses and freezes therein. Even in an air pump for supplying air to an oxygen electrode of the fuel cell stack, there is also fear that moisture in introduced air or a backflow of humidification air from an exhaust-side causes freeze inside the air pump.
If a roots pump shown in FIG. 4 is adapted for the hydrogen pump or the air pump, the moisture remains in a space between a pair of rotors 21, or in a space between each rotor 21 and a casing 22, and freezes therein due to surface tension of water. If the moisture freezes in the surface of each rotor 21, there is fear that the roots pump is not capable of being started upon restarted.